Texture fills show in the vector tab as soon as they load (#196)

After signing out and back in, a texture fill stayed in its base
colour until something else redrew the vector tab. The texture
library is a singleton that outlives the editor. Four widgets
subscribed to it and never unsubscribed. After a new sign-in the
first loaded texture called a destroyed canvas, which threw and
stopped the loop before the vector tab heard about the image.

- TextureCanvas, TileCanvas, ShaderPreview and WorldViewport now
  unsubscribe in destroy(). This is the pattern FontPreview and
  VectorArtCanvas already use. WorldViewport leaves both the
  texture and the font library.
- FileLibrary.notifyChange catches errors per listener. A broken
  listener no longer starves the others. The error is still
  logged as "[textures] a listener failed".
- e2e 47i no longer forces a redraw. It waits up to 3 s for the
  tab to show the texture on its own.

Findings:
- The trigger was e2e module 45 (sign out, sign in), not the
  texture fill. My note in #196 that the browser showed no
  exception was wrong. The counter-check shows it clearly.

Tests:
- ./check.sh: 137 files, 2051 tests, exit 0 (before 136 / 2049)
- 2 new unit tests in tests/viewport/file-library.test.ts
- GM_STEPS=45,47 after a fresh seed: ALL PASSED, 71 checks
- Counter-check with the old source and the new check: 1 FAIL
  (shape stays #0000ff) plus the TypeError. Old FileLibrary.ts
  fails the first unit test.
- No full e2e run locally. The check count is unchanged.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/editor/shader/ShaderPreview.ts

@@ -32,6 +32,7 @@ export class ShaderPreview extends Widget {
   private clockOrigin = 0;
   /** Null: the clock runs. A number: the preview stands at that second. */
   private held: number | null = null;
+  private readonly stopPictures: () => void;
 
   constructor(private readonly state: EditorState) {
     super();
@@ -39,7 +40,7 @@ export class ShaderPreview extends Widget {
     this.content.addChild(this.mesh);
     this.content.mask = this.clip;
     this.addChild(this.bg, this.content, this.clip);
-    textureLibrary.onChange(() => this.invalidate());
+    this.stopPictures = textureLibrary.onChange(() => this.invalidate());
   }
 
   override measure(): Size {
@@ -107,6 +108,7 @@ export class ShaderPreview extends Widget {
   }
 
   override destroy(): void {
+    this.stopPictures();
     disposeSpriteMesh(this.mesh);
     super.destroy();
   }

src/editor/texture/TextureCanvas.ts

@@ -136,6 +136,7 @@ export class TextureCanvas extends Widget {
   private collision = false;
   /** The outline a click adds corners to; for another frame, or one gone, the frame's last one. */
   private active = { frameId: '', index: -1 };
+  private readonly stopPictures: () => void;
 
   constructor(private readonly state: EditorState) {
     super();
@@ -159,7 +160,13 @@ export class TextureCanvas extends Widget {
       this.redraw();
     });
     // A picture arrives asynchronously; until then there is nothing to fit the view to.
-    textureLibrary.onChange(() => this.redraw());
+    this.stopPictures = textureLibrary.onChange(() => this.redraw());
+  }
+
+  /** The library outlives a signed-out editor; a stale listener would redraw destroyed graphics. */
+  override destroy(options?: Parameters<Widget['destroy']>[0]): void {
+    this.stopPictures();
+    super.destroy(options);
   }
 
   override measure(): Size {

src/editor/tile/TileCanvas.ts

@@ -68,6 +68,7 @@ export class TileCanvas extends Widget {
   private board = { w: 0, h: 0 };
   private info: TileInfo | null = null;
   private needsFit = true;
+  private readonly stopPictures: () => void;
 
   constructor(private readonly state: EditorState) {
     super();
@@ -90,7 +91,13 @@ export class TileCanvas extends Widget {
     state.on('project', () => this.redraw());
     state.on('load', () => this.show(''));
     // A picture arrives asynchronously; the board is empty until it does.
-    textureLibrary.onChange(() => this.redraw());
+    this.stopPictures = textureLibrary.onChange(() => this.redraw());
+  }
+
+  /** The library outlives a signed-out editor; a stale listener would redraw destroyed graphics. */
+  override destroy(options?: Parameters<Widget['destroy']>[0]): void {
+    this.stopPictures();
+    super.destroy(options);
   }
 
   override measure(): Size {

src/editor/viewport/WorldViewport.ts

@@ -61,6 +61,7 @@ export abstract class WorldViewport extends Widget {
   private visibleCount = 0;
   private animated = false;
   protected lastItems: DrawItem[] = [];
+  private readonly stopFiles: (() => void)[];
 
   protected constructor(protected readonly state: EditorState) {
     super();
@@ -78,8 +79,16 @@ export abstract class WorldViewport extends Widget {
       if (this.visible && !this.animated) this.redraw();
     });
     // Unconditional: a picture or a typeface arriving fires once per file, not per frame.
-    textureLibrary.onChange(() => this.redraw());
-    fontLibrary.onChange(() => this.redraw());
+    this.stopFiles = [
+      textureLibrary.onChange(() => this.redraw()),
+      fontLibrary.onChange(() => this.redraw()),
+    ];
+  }
+
+  /** The libraries outlive a signed-out editor; a stale listener would redraw destroyed graphics. */
+  override destroy(options?: Parameters<Widget['destroy']>[0]): void {
+    for (const stop of this.stopFiles) stop();
+    super.destroy(options);
   }
 
   override measure(): Size {

src/viewport/FileLibrary.ts

@@ -30,7 +30,13 @@ export abstract class FileLibrary<T> {
 
   /** Runs the listeners: something they draw from has changed without a file arriving here. */
   notifyChange(): void {
-    for (const listener of this.listeners) listener();
+    // One listener that throws must not keep the file from the ones after it (#196).
+    for (const listener of this.listeners)
+      try {
+        listener();
+      } catch (error) {
+        console.error(`[${this.tag}] a listener failed`, error);
+      }
   }
 
   protected abstract fetchFile(url: string, file: string): Promise<T>;